Recombinant DNA technology has provided substantial improvements in the safety, quality, efficacy and cost of pharmaceutical and veterinary medicaments including vaccines. Plant produced mucosal vaccines were invented by Curtiss & Cardineau. See U.S. Pat. Nos. 5,654,184; 5,679,880 and 5,686,079 herein incorporated by reference. Others have described transgenic plants expressing immunoprotective antigens and methods for production including Arntzen, Mason and Lam. See U.S. Pat. Nos. 5,484,717; 5,914,123; 6,034,298; 6,136,320; 6,194,560; and 6,395,964 herein incorporated by reference.
Vaccines produced in plant systems offer a number of advantages over conventional production systems. Conventionally produced vaccines strains (live and vectored) may revert towards virulence or carry biological contaminants from the production process. Subunit vaccines may be difficult to produce and purify due to protein instability issues and will not be glycosylated when produced in prokaryotes.
Plant cell production avoids the need for animal-sourced components in growth media essentially eliminating the risk of transmitting pathogenic contaminants from the production process. Plant cells are capable of post translational glycosylation, and plant cell growth media is generally less expensive and easier to handle and prepare compared to conventional growth media presently used in the manufacture of vaccines.
Systemic immunity to a particular pathogen results from activation of the immune system in response to antigen presented by a particular pathogenic organism or via a vaccine designed to protect against a particular pathogenic agent. Exposure to a pathogen is often through mucosal surfaces that are constantly exposed and challenged by pathogenic organisms.
Mucosal and oral immunity results from the production of sIgA (secretory IgA) antibodies in secretions that bathe all mucosal surfaces of the respiratory tract, gastrointestinal tract and the genitourinary tract and in secretions from all secretory glands. McGhee, J. R. et al., Annals N. Y. Acad. Sci. 409, (1983). These sIgA antibodies act to prevent colonization of pathogens on a mucosal surface (Williams, R. C. et al., Science 177, 697 (1972); McNabb, P. C. et al., Ann. Rev. Microbiol. 35, 477 (1981) and thus act as a first line of defense to prevent colonization or invasion through a mucosal surface. The production of sIgA can be stimulated either by local immunization of the secretory gland or tissue or by presentation of an antigen to either the GALT (gut-associated lymphoid tissue or Peyer's patches) or the BALT (bronchial-associated lymphoid tissue). Cebra, J. J. et al., Cold Spring Harbor Symp. Quant. Biol. 41, 210 (1976); Bienenstock, J. M., Adv. Exp. Med. Biol. 107, 53 (1978); Weisz-Carrington, P. Et al., J. Immunol 123, 1705 (1979); McCaughan, G. et al., Internal Rev. Physiol 28, 131 (1983). Membranous microfold cells, otherwise known as M Cells, cover the surface of the GALT and BALT and may be associated with other secretory mucosal surfaces. M cells act to sample antigens from the luminal space adjacent to the mucosal surface and transfer such antigens to antigen-presenting cells (dendritic cells and macrophages), which in turn present the antigen to a T lymphocyte (in the case of T-dependent antigens), which process the antigen for presentation to a committed B cell. B cells are then stimulated to proliferate, migrate and ultimately be transformed into an antibody-secreting plasma cell producing IgA against the presented antigen. When the antigen is taken up by M cells overlying the GALT and BALT, a generalized mucosal immunity results with sIgA against the antigen being produced by all secretory tissues in the body. Cebra et al., supra; Bienenstock et al., supra; Weinz-Carrington et al., supra; McCaughan et al., supra. Oral immunization is therefore a most important route to stimulate a generalized mucosal immune response and, in addition, leads to local stimulation of a secretory immune response in the oral cavity and in the gastrointestinal tract.
Mucosal immunity can also be advantageously transferred to offspring. Immunity in neonates may be passively acquired through colostrum and/or milk. This has been referred to as lactogenic immunity and is an efficient way to protect animals during early life. sIgA is the major immunoglobulin in milk and is most efficiently induced by mucosal immunization.
The M cells overlying the Peyer's patches of the gut-associated lymphoid tissue are capable of taking up a diversity of antigenic material and particles (Sneller, M. C. and Strober, W., J. Inf. Dis. 154, 737 (1986). Because of their abilities to take up latex and polystyrene spheres, charcoal, microcapsules and other soluble and particulate matter, it is possible to deliver a diversity of materials to the GALT independent of any specific adhesive-type property of the material to be delivered.
Vectors and cells useful for producing transgenic plant-derived immunoprotective antigens, and improved methods of antigen production would greatly facilitate the development, manufacture and efficacy plant-produced vaccines.